North Korean leader Kim Jong Il, viewing farms and fields during his visit to the Sinam Cooperative Farm in Ryongchon County, North Korea.

In the heart of Pyongyang stands a gray, six-story concrete building that is not unlike thousands of others in the dreary communist capital, except that this one is protected around the clock by uniformed soldiers. The building is known as Bureau 39, and it is the headquarters of a worldwide criminal enterprise that is owned, overseen and operated by the government of North Korea.

Through a state-owned conglomerate called Daesong, Bureau 39 oversees export businesses owned and run by the North Korean government--mainly textile and other light-manufacturing factories and some mines. But Bureau 39 also houses another, shadowy directorate that oversees...